(a) Field of the Invention
The present invention relates to an apparatus and method for time synchronization, and more particularly, to an apparatus and method for time synchronization of a femtocell base station.
(b) Description of the Related Art
The types of mobile communication services are rapidly shifting from conventional voice to data, and data traffic is expected to grow rapidly as smartphones proliferate. Therefore, a femtocell appeared as a way of making efficient use of limited frequency resources, based on the idea that a small base station is installed in a home in order to increase service capacity by shortening the radio reaching distance of a base station.
However, a femtocell base station is generally installed in a building, and therefore shows significantly low performance in receiving a time information signal from a conventional GPS satellite. Thus, the problem of synchronization with an existing base station (e.g., a macrocell base station) arises.
To solve this problem of synchronization, a variety of synchronization acquisition methods have been devised. These methods include an Assisted GPS method for receiving information about a GPS satellite, such as Almanac data, ephermeris data, etc from an assistance server through a wired network, a wireless connection technology-method for receiving and using a synchronization radio signal from a neighboring macrocell base station, and a network-based method using a network synchronization protocol, such as a PTP (Precision Time Protocol).
Among these various types of synchronization methods, the assisted GPS method or the wireless connection technology-based method requires additional high costs in terms of the implementation of a femtocell base station. Thus, the network-based method, which can be implemented at relatively low costs, has been favored up to now.
The conventional network-based method is realized through the reception of time information provided by a PTP (Precision Time Protocol) and an NTP (Network Timing Protocol) protocol according to the IEEE 1588 standard which were developed as a way of synchronization of an asynchronous network such as Ethernet, in order to maintain time synchronization with a conventional macrocell base station.
This network-based method is a method in which a timing server connected to a wired internet network transmits a timing packet through the wired internet network and a femtocell base station, a client, extracts a synchronization signal contained in the received timing packet.
However, the accuracy of synchronization of the network-based method depends largely on imbalance between uplink and downlink packet delays that a non-dedicated line service such as x-DSL or FTTH involves. That is, packet transmission delay increase irregularly due to an increase in traffic volume on an asynchronous network for timing packet transmission, synchronization errors become larger in proportion to the number of femtocells and the size of the network.